Update on cam variation- need the experts!

[Gary_d]

First thing is, yes the car is off the road and garaged until fixed at this point.

I had a problem with bank 1 throwing a 1531 code. Durametric told me the solenoid wasn't working. Cleaned the wiring contacts and that seemed to fix that problem. I've been running a steady -6 on both sides (in spec), but bank 1 would still throw the code now and then.
I took a 20 mile run the other day with the laptop hooked up (had to pick up the wife), and both banks held a steady -6 for the first mile, then bank 1 changed to -4 and held. Unhooked the Durametric for her to ride, by the time I got home I had the CEL on again, same code.

Today I hooked it up again and went for an errand. Bank 1 started out at -4. About 2 miles into the run it had changed to +12. Stopped, did my shopping and refired the car. Now the variation showed +18, definitely where the code was coming from. That held steady all the way home (2 miles).

The question is, how would it change from a -6 to a -4 then a +18? If the chains were jumping time, wouldn't it keep heading in the same direction - or +?
Only happens on bank 1 too, bank 2 is still a steady -6 (omits the intermediate shaft shifting).